Barely Holding On
by Alive Through Writing
Summary: Agent Cynthia 'Sin' Stark of S.H.I.E.L.D. joins the Avengers to fight off the mutant vampires, werewolves and zombies created by a man out for revenge, but with her biological father coming to help and Clint stealing her attention, will she be able to stay focused enough to save New York? Clint/oc, Tony's adopted sister, Dr Strange's daughter. (Subject to changes)
1. Chapter 1

"We have a serious problem" the imposing man spoke to the odd group standing in a lounge in Stark Tower.

"Obviously," Tony Stark spoke from the doorway, "otherwise you wouldn't be here. In case you hadn't noticed, it's Halloween, it's kinda a tradition in this place to celebrate, thus the decorations" he points to the elaborate yet fun black and orange theme the room currently had, with the occasional toy spiders hanging off furniture and walls.

"Tony" a young brunette glares warningly from the black leather couch where she sits next to Natasha Romanov. "My apologies for Tony, Director, please, continue" back to her professional stance.

"As I was saying, we have a serious problem. Staten Island has been overrun by" Director Fury stopped himself, looking around the group before sighing and continuing, "overrun by vampires, zombies and werewolves"

The group was silent, looking from one to another attempting to figure out if Fury was being serious or not before Tony laughed out loud.

"Good try, Fury, but April Fool's day is, as it says, in April" patting the Director once on the shoulder before making his way towards the arm of the couch next to the brunette woman who rolls her eyes.

"I'm sorry, sir, but could you explain?" the woman asks cautiously, ignoring Tony.

"Wait, Sin, you're actually going along with this?" Tony asks in disbelief, looking to his friends who were in thought.

"Yes, Tony, I have never, in seven years of working for him, seen him make a joke, no offence sir, and I highly doubt he would come here, of all places, just to do so" Cynthia replies.

Handing each of the rooms occupants a manilla folder, Fury continues. "An Austrian scientist by the name of Heinrich Herceg is claiming responsibility, however his, for lack of a better word, mutants, are protecting him. No matter how we try to get to him, they stop us. This is where you all come in. I believe that if you stop Herceg, you can stop his army, having said this, there are already hundreds of his mutants in Statten Island attacking civilians."

"Alright, so how do we kill 'em?" Steve Rodgers asks from his spot on the opposite couch to Cynthia and Natasha.

"Well, that's the problem the vampires can be killed by a stake to the heart or fire, the werewolves by fire or silver and the zombies by decapitation."

"So there isn't one way to kill them all?" Clint asks eyebrow raised slightly. While he had begun to accept the whole Loki and aliens thing, vampires, werewolves and zombies were another thing.

"Unfortunately not, therefore you will be working in groups. Rogers, Stark and Banner, you'll be on perimeter, I want as many of these guys taken out as possible before Herceg is captured. Barton, Romanov, you'll be assisting Cynthia in capturing Herceg. Anyone gets in your way, you take them out" Fury instructs.

"Wait just one second," Tony complains, "Cynthia is not doing this".

"Actually, Tony, I think you'll find I am. Cynthia smirks lightly.

"Stark, I know you are worried for your sister, but she is more than capable for this assignment" Natasha adds, "I've worked with her before and I have to agree with Fury, she's the best person for it, she can destroy any of the three types and we'll need that to get Herceg".

"I've also asked another to join you, however he may not be able to get here in time..." the Director drifts off.

"Oh?" Steve looks up intrigued, watching Cynthia get up out of the corner of his eye and argue quietly with her brother in a corner.

"A Dr. Stephen Strange."

"What?!" Cynthia yells, ignoring the fight she had been quietly engaged in with Tony. The room turns to look at Cynthia, surprise on all their faces excluding Tony and Director Fury. "He... He's coming back?" her voice breaks slightly, showing the hope she was trying to hide.

"He said, and these are his words "I have defended worlds far from here, and times yet to come, it is now my turn to defend that which matters most"" The Director finishes in a soft tone looking at the usually well composed agent in front of him slowly crumble, before nodding once and leaving the Tower.

"Um, I have to... Excuse me" Cynthia stuttered before walking out the room towards her floor, looking at the ground as she left.

"Um," Bruce breaks the silence, "shouldn't someone check on her?"

"No, trust me, she needs some time to compute this" Tony replies quieter than normal.

"Sorry," Clint starts, "but, what just happened?"

"Strange is her biological father" Tony replies, still in a quiet tone before walking out in the opposite direction to his sister.

"Well that was..."Steve starts.

"Odd" Bruce finishes for him as the four sit awkwardly.

"Stuff Tony, I'm going to see if Sin is ok" Natasha says, hurrying after her friend.

Only seconds later, Bruce takes his leave to check on Tony, leaving Steve and Clint to puzzle over what just happened.


	2. Chapter 2

Twenty minutes later, Clint finds himself sitting by himself in the lounge, Steve having departed to do some boxing shortly after Bruce leaving. It was times like these he craved. No crazy shenanigans from Tony, no need to be social, he could just relax. He sighs, so why wasn't he enjoying this peace? Most likely the upcoming battle, Clint reasons to himself as he slowly sips his bottle of water before resting his head against the back of the sofa.

"Damn it!" Clint wakes from his doze to here his partners voice yell, looking over to the red-haired agent as she grumpily throws herself back into the couch she had previously been seated in. Clint doesn't question her, merely raising an eye.

"I can't find her anywhere! She's not in her room, or the gym, not even the library!" she states flopping down on the couch so she's now lying there.

"Um, did you try JARVIS?" Clint asks cautiously. "JARVIS, do you know where Cynthia went?" he asks casually.

"I'm afraid Ms Stark has taken one of the cars and is currently out 'clearing her head' as she puts it, Mr Barton" the British voice answers over the speakers.

"Any idea when she might be back?"

A short wait comes before JARVIS replies, "Ms Stark asks that you give her a little time and that she'll be back some time today"

"Ok, there you go, Nat, she'll be back later, she probably just needs to clear her head" Clint looks over to Natasha who has regained her composure and is sitting upright again.

"You're right, she'll be fine" Natasha says, more to herself than Clint.

* * *

At 11:59 pm, Cynthia stumbles through the elevator towards the small kitchenette on the top floor, making her way slowly, and not so surely towards a large glass of water and some painkillers. But before she can get there the bright main lights come on.

"Fuck!" she swears, "JARVIS, turn down the blasted lights!" she slurs slightly.

"Ignore that" Tony counters from the couches.

"Aw crap" Cynthia mumbles to herself looking towards her brother.

"What the hell, Cynthia, you leave mid-morning upset, we don't see you or hear from you and now you arrive in the middle of the night _drunk?" _

"Coming from you, that's a bit rich, don't you think?" Cynthia replies, attempting to look stern.

"This isn't about me, Sin"

"Oh bull, what isn't?"

"Sin, we were worried, we all were" Cynthia rolls her eyes at this. "I mean it, even Katniss started to worry"

Cynthia rolls her eyes again before gulping down the tablets and water. "Tony, I told JARVIS I just needed some time"

"And some alcohol apparently" Tony remarks.

"I'm going to bed, I'll see you in the morning" Cynthia replies ignoring his last statement and walking down the hall towards her room.

Sighing to himself, Tony watches her retreating form. This was going to be draining and not just because of the impending battle.

* * *

**Author's Note: **Ok, so I know that was boring as hell, but I needed to get SOMETHING up, and I didn't want to write anything big whilst I sat here at work, sorry that it's only a bit of a filler, but I promise to write at least 1 more chapter over this weekend. Thank you all :)


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